Oneiris is a mythological entity that supposedly created the World of Dream, and is the source of all Light in the world.
In Kendall's Quatre
Oneiris is the second-eldest of the four siblings. He sought to give the world something to hope for, and argued with his younger sister, Mnemosyne, that the world needs hope than it does the ability to cherish what once was. The two clashed, and became their own worlds, whose energies flow into the main world.
In the real world
Oneiris (the world) is suspected to indeed be influenced by a sentient individual. What influence there may be, or if this is even correct, is unknown.